Incision of human skin is common practice in the clinical environment, for example during surgery, taking blood or on insertion of intravascular devices such as catheters. Hospital acquired infections are frequent complications following incision of the skin, particularly when intravascular devices are inserted, and are commonly associated with skin microorganisms, for example Staphylococcus epidermidis (Richards, et al., 2000; Pfaller, et al., 1999; Rupp and Archer 1994).
Several factors contribute to establishment of the infection, for example inadequate skin disinfection prior to skin penetration (Lafforgue, at al., 1997; Traore, et al., 2000; Langgartner, at al., 2004) and the emergence of resistant microorganisms within the clinical setting, often due to the wide use of antimicrobial agents including antibiotics, antiseptics and other biocides (Koljalq, at al., 2002; Fraise, 2002; Block and Furman, 2002).
Microorganisms may exist as microcolonies within the skin or as biofilms in situ on intravascular devices, for example on the surface of a catheter, and are therefore more resistant to higher concentrations of antimicrobials compared to microorganisms in suspension (Rupp and Archer, 1994; Gristina, at al., 1989; Saginur, et al., 2006).
Many antimicrobials are known for the treatment of skin infections. For example, chlorhexidine is known to have a broad range of antimicrobial activity, with rapid action, suitable for skin preparation prior to invasive procedures such as CVC insertion (McDonnell and Russell, 1999).
Some essential oils have also been shown to have antimicrobial activity with efficacy against bacteria, yeast and viruses (Cowan, 1999; Karpanen, et al., 2006). Tea tree oil (TTO) has also been shown to be effective in eradicating MRSA colonization (Al-Shuneigat, at al., 2005; Dryden, at al., 2004; Caelli, et al., 2000) and reducing microbial contamination of hands (Messager, et al., 2005). Other essential oils including eucalyptus and thymol have also been investigated for their potential clinical applications; thymol has been shown to have anti-inflammatory properties and increase wound healing in burns (Dursun, et al., 2003) and eucalyptus was found to improve healing of necrotic ulcers (Warnke, et al., 2006).
The combination of an essential oil with chlorhexidine digluconate is known. Antimicrobial effects of combinations of essential oils with chlorhexidine digluconate against oral pathogens Streptococcus mutans and Lactobacillus plantarum have been studied (Flioche, et al., 2005), with a view to development of novel anticaries treatments. US 2006/0105000 describes compositions for treating infected skin and mucosal membranes comprising an anti-microbial agent and an essential oil. Chlorhexidine gluconate was used as the anti-microbial agent in a mucositis mouthwash, an anal fissure gel and a pressure sore wash.
Despite the wide range of available antimicrobials, a number of antimicrobials, including chlorhexidine, are known to show poor permeability into the skin, so bacteria deeper in the skin or beneath the surface of the skin and in the hair follicles often remain unaffected by current methods of skin disinfection. Therefore infections, in particular those in the skin, remain a problem, as the antimicrobial cannot penetrate the skin.
New methods for delivering skin antiseptics have been explored, such as liposomes, microparticles and nanoparticles, which would provide targeted and controlled release of antimicrobial agents (Constant, et al., 2006). Essential oils have also been studied as skin permeation enhancers (Biruss, et al., 2007; Reichlich, et al., 2006; Fang, et al., 2004). However the effectiveness of essential oils as permeation enhancers is limited because the ability of an essential oil to increase permeation through the skin is drug specific. Therefore, there remains a general need for improved antimicrobials, in particular for methods and products for preventing and treating sub-cutaneous infections.